7A52铝合金MIG焊接头的X射线衍射分析

X-ray diffraction analysis of 7A52 aluminum alloy MIG welded joint

采用微合金化Ml—Mg—Mn—Sc—Zr合金焊丝按MIG方法焊接7A52铝合金板材。采用高功率X射线衍射仪对7A52铝合金焊接接头不同部位进行了精确的X射线衍射分析。结果表明，在焊接接头中存在四个本质的热扩散区域。离焊缝中心线0～4mm范围为焊缝区，焊缝中心为铸态组织；4～10mm区域为半熔化区，在自然时效过程中有较多微小的强化相η＇析出；10～16mm范围为淬火区，原有沉淀相部分地回溶到基体并不能在自然时效过程中重新析出；最远端为软化区，基材中原有强化相叩在焊接热输入的影响下形成了粗大的T相，导致强度降低。焊接热输入对不同区域的影响大小不同，导致不同区域的固溶程度和晶格畸变量不同，从而使微观和宏观残余应力都略有差异。

7A52 alloy plate was welded by means of MIG(metal inert-gas) welding using Al-Mg-Mn-Sc-Zr micro-alloyed wire.The specimens cut down at different regions of the welded joint were diffracted accurately by high-power X-ray diffractometer.The results showed that there are 4 different heat diffusion zones in the welded joint,these zones had themselves substantive characteristics.The first was the weld,and it was the α-Al matrix as cast structure distanced the weld centre line about 0-4 mm.The second was the semi-melted zone,and it distanced the weld centre line about 4-10 mm.The nanocrystalline η′(MgZn2) phase and Al6Mn re-precipitated in nature ageing process when it was laid at room temperature.The region distanced the weld centre 10-16 mm was the low temperature solution zone,and the strengthening phases redissolved into α-Al matrix partly at the weld temperature but could not re-precipitate at room temperature.The fourth was a soften zone.In this zone,the strengthening phase growth and formed the T phase.It was the reason of strength decreasing.Because the effects of welding heat on zones were different,it lead to different solid solubility,distortion of lattice,the micro-strains and residual stress.